Pharmacokinetics encompasses the absorption of cannabinoids following diverse routes of administration and from different drug formulations, the distribution of analytes throughout the body, the metabolism of cannabinoids by different tissues and organs, the elimination of cannabinoids from the body in the feces, urine, sweaty oral fluid, and hair, and how these processes change over time. Cannabinoid pharmacokinetic research has been especially challenging because of low analyte concentrations, rapid and extensive metabolism, and physio-chemicaI characteristics that hinder the separation of drugs of interest from biological matrices and from each other, and that lower drug recovery because of adsorption of compounds of interest to multiple surfaces. Mass spectrometric developments now permit highly sensitive and specific measurement of cannabinoids in a wide variety of biological matrices.